OBJECTIVE To describe leukocytosis trends during cervical preparation with osmotic dilators for second-trimester dilation and evacuation procedures, and to determine whether there is a difference in leukocytosis seen with laminaria versus Dilapan-S. METHODS We conducted a retrospective cohort study of 986 women presenting for dilation and evacuation from April 2008 through March 2009 at an outpatient clinic network. We included all procedures at ⩾14 weeks' gestation where laminaria or Dilapan-S dilators were used for overnight dilation. All women had routine white blood cell testing during the study period. RESULTS There was a median increase of 2.4 × 103/μL white blood cell count (95% confidence interval 2.2-2.7 × 103/μL) from beginning of cervical preparation to the day of procedure (95% confidence interval and p value). Women receiving laminaria (n = 805) versus Dilapan-S (n = 181) had a greater increase in white blood cell count from baseline (median increase 2.7 versus 1.2 × 103/μL, p < 0.001), including when adjusting for age, gestational age, parity, baseline white blood cell count, and number of dilators placed. CONCLUSIONS There is increased leukocytosis during the course of cervical preparation with osmotic dilators, and this is increased with use of laminaria versus Dilapan-S. Rates of clinically recognized infection in second-trimester abortion are low regardless of dilator type used.